do not hardcode version to test

test/distrib/csharp/run_distrib_test.sh

@@ -34,8 +34,9 @@ cd $(dirname $0)
 
 unzip -o "$EXTERNAL_GIT_ROOT/input_artifacts/csharp_nugets.zip" -d TestNugetFeed
 
-# TODO(jtattermusch): replace the version number
-./update_version.sh 0.13.0
+# Extract the version number from Grpc nuget package name.
+CSHARP_VERSION=$(ls TestNugetFeed | grep '^Grpc\.[0-9].*\.nupkg$' | sed s/^Grpc\.// | sed s/\.nupkg$//)
+./update_version.sh $CSHARP_VERSION
 
 nuget restore